Cancer is one of the major causes of human morbidity and mortality. Cancer treatment is challenging because it is difficult to kill cancer cells without damaging or killing normal cells. Damaging or killing normal cells during cancer treatment causes adverse side effects in patients and can limit the amount of anticancer drug administered to a cancer patient. It is also difficult to kill cancer cells in regions distant from the vasculature where anticancer drugs fail to penetrate.
Many cancer cells are more hypoxic relative to normal cells. Tumor hypoxia is associated with resistance to anticancer therapies, cancer relapse, and poor prognosis. Certain drugs in preclinical and clinical development target hypoxic cancer cells. These drugs, called hypoxia-activated prodrugs or “HAPs” are administered in an inactive, or prodrug, form but are activated, and become toxic, in a hypoxic environment. US 2010/0137254 and US 2010/0183742, each of which is incorporated herein by reference, describe HAPs such as those having a structure defined by formula (I), below:
where Z3 is selected from the group consisting of:
and X4 is Cl or Br.
The compounds known as TH-302 and TH-281 are particularly promising therapeutic candidates. TH-302 (see Duan et al., 2008, J. Med. Chem. 51: 2412-2420, incorporated herein by reference), known by the chemical name (2-bromoethyl)({[(2-bromoethyl)amino][(2-nitro-3-methylimidazol-4-yl)methoxy]phosphoryl})amine, has the structure represented below:

Another promising HAP is TH-281, which differs from TH-302 only in that it has 2-chloroethyl groups instead of the 2-bromoethyl groups present in TH-302.
However, while nearly all tumors contain hypoxic regions, there is a wide variability among patients in how hypoxic a tumor of a given cancer type may be. For example, using median tumor pO2 (mm Hg) as a measure of tumor hypoxia, one study of 33 soft tissue sarcoma patients showed that the median tumor pO2 ranged from about 1 to about 70 mm Hg (see Nordsmark et al., 2001, Brit. J. Cancer 84(8): 1070-1075). Another study of 58 head and neck cancer patients showed the hypoxic fraction ranged from just above 90% to 1%. Thus, if greater tumor hypoxia correlates with a better response to HAP-mediated anti-cancer therapy, then this variability in tumor hypoxia will translate into a variable response to HAP anti-cancer therapy.
“Biomarkers” generally refers to biological molecules, and quantitative and qualitative measurements of the same, that are indicative of a disease state. “Prognostic biomarkers” correlate with disease outcome, independent of therapy. For example, tumor hypoxia is a negative prognostic marker—the higher the tumor hypoxia, the higher the likelihood that the outcome of the disease will be negative. “Predictive biomarkers” indicate whether a patient is likely to respond positively to a particular therapy. For example, HER2 profiling is commonly used in breast cancer patients to determine if those patients are likely to respond to Herceptin® (trastuzumab, Genentech). “Response biomarkers” provide a measure of the response to a therapy and so provide an indication of whether a therapy is working. For example, decreasing levels of prostate specific antigen (PSA) generally indicate that anti-cancer therapy for a prostate cancer patient is working.
Hypoxia results in a number of biological responses mediated by hypoxia signal transduction pathways. Two of the primary hypoxia signal transduction pathways are the HIF (hypoxia inducible factor) pathway and the UPR (unfolded protein response) pathway. CYP2W1 (cytochrome P450, family 2, subfamily W, polypeptide 1) is an extra-hepatic cytochrome P450 enzyme that has a unique tumor-specific expression pattern (see Gomez et al., 2010, Mol. Pharmacol 78: 1004-1011; Karlgren et al., 2006, Biochem Biophys Res Comm 341: 451-458). Moreover, CYP2W1 has previously been shown to be able to reduce and activate another hypoxia-targeted prodrug called AQ4N (Nishida et al., 2010, Mol Pharmacol 78: 497-502).
There remains a need for new methods of determining whether a cancer patient is likely to respond favorably to treatment with hypoxia-activated achiral phosphoramidate mustards, such as TH-302, and/or to treat such patients. The present invention meets these needs.